Lecture#2

Naming

First symbol

_ (underscore) or letter

Symbols

_ (underscore), letters, digits

_myfunc __somemagic generate_file generate-file 6func fancy#name

Numbers

Integer

32 bit -2147483648...2147483647 long - arbitrary

boolean - True, False

Float

double precision, no support for single precision

Complex

two double precision numbers

Sequences

List (mutable)

[1,2,”Hello World”, True]

Tuple (immutable)

(1,2,”Hello World”, True)

String (immutable)

“HPC”, ‘new string’, ‘’’Some multiline string’’’

Mappings

Dictionary (mutable)

key-value storage

my_dict = {‘a’:2, ‘string’:42, (1,2,3): [1,2,3]} my_dict[‘a’] == 2 #True

my_dict[(1,2,3)] == [1,2,3] #True

Only immutable types can be a key

Logic

and, or, not

non-zero numbers, non-empty objects: True zero-numbers, empty-objects, None: False comparison and equality: True or False and, or: return operand

if … elif ... else statement

a if b else c statement

Blocks

Blocks are intended (with spaces, not tabs!) if x > y:

print “x > y”

x = y

elif x == y: print “X = Y” else: print “X < Y”

Empty block: pass

Linebreaks

Break the line:

x = [1, 2, \ 3,4]

a = ‘’’Some multiline string’’’

x = [1, 2, 3,4]

x = (1, 2, 3,4)

x = {‘a’:1, ‘b’:4)

x = {‘a’:1, ‘b’:4)

Iterations

for i in some_iterable: do_something(i)

some_iterable:

list, tuple, string, set, other iterable objects

while (x > 5):

do_something(x) x += 1

Functions

def my_func(a, b=None):

print ‘a and b are positional arguments’ print ‘b has default value’

my_func(1) #the same as my_func(1, None) my_func(1, 2)

Can have variable number of arguments

Files

f = open(filename, mode), f.close()

mode:

‘r’ - read (default),

‘w’ - write (existing file is erased), ‘a’ - append,

‘r+’ - read and write

f.read() or f.read(size) #read entire file (be careful) or size bytes

f.readline() #read line

Iterate over file: for line in f:

print line